CREATING an opera based on real-life events is nothing new: think of the historical operas of Handel, Rossini or Verdi; and more recently Nixon in China or The Death of Klinghoffer. The difference between the earlier and the later ones is that Nixon and Klinghoffer recount events within living memory, with people, or their families and friends, who may still be alive.

Hence the controversy - before a note was heard - surrounding Between Worlds, a new opera by the composer Tansy Davies, librettist Nick Drake, and director Deborah Warner, which received its world première by the English National Opera at the Barbican Theatre last week, to be followed by several further performances there until Saturday 25 April.

The subject is 9/11 and the destruction of New York's World Trade Center - the "Twin Towers" - not a subject for entertainment, according to many with connections to this terrible disaster. But the opera was announced by the ENO as "spiritual, poetic and ultimately uplifting", and the healing power of music is surely universally recognised.

The worlds of the title are life and death. The subject is, of course, huge; so what we see and hear is a microcosm of this unspeakable event. "Music is a fantastic vehicle for expressing energy, emotion, feelings that go beyond language," Davies says, and Nick Drake agrees: "Music in the end moves us beyond what is sayable into the unsayable, and that's where we need to go with a story like this."

This is not a sensationalist opera. In fact it begins almost imperceptibly, with the janitor of one of the floors of the North Tower pausing to contemplate the spectacular view over New York and watching the dawn break. He is extending his night shift to help set up the room for a meeting. A figure of calm reassurance, he remains so throughout the events that follow.

All the characters are fictional and nameless, and the action is presented on three levels. On the floor of the stage are the people going about their normal lives, looking forward to a good day. But the mundane occurrences - the man's argument with his wife, the troublesome child who will not say goodbye to his mother before she goes to work, the parting of two lovers, the excitement of the young man, new to the city - are to assume great significance when they find themselves at the point of no return in the Tower.

When this moment arrives - in the office on a higher level of the stage - time opens out, so that what would have taken place simultaneously, and within a very short period throughout both buildings, is slowed down so that the thoughts and reactions of the four featured victims - attempting to make contact with their loved ones, and grappling with the realisation that they are not going to survive - is given a prominence to which the destruction of the towers becomes merely the background.

Over all this a shamanic figure (a countertenor) presides at the highest point of the stage, the janitor being the only one who appears to have any inkling of his presence, and for whom he becomes a spirit guide.

The orchestra provides a reassuring undercurrent throughout, perhaps suggesting the palm of God's hand; and indeed, as the Firemen realise the enormity of the situation, they sing from the requiem mass; and the victims in the office, as the end comes, sing from Psalm 130, "Out of the Deep". Ultimately, on all levels, the power of darkness is matched with light.

The words are crucial, but throughout much of the performance were not as clearly projected as they should have been, one exception being Susan Bickley as the Mother of the Younger Man, very touching in her incomprehending desolation.

Nevertheless, Between Worlds still comes across as a very powerful piece, brilliantly conceived and presented, which will surely grow with greater familiarity. Davies has, as she herself wished, "[turned] something very complex and difficult into something healing and beautiful", demonstrating the enduring, transcending power of love and the power of music to express it.

Further performances of Between Worlds at the Barbican Theatre, Silk Street, London EC2, are tonight at 7.30 p.m., Sunday at 3 p.m, and 21, 23, and 25 April at 7.30 p.m. Tickets exclusively from Barbican Box Office: 020 7638 8891.

www.eno.org/whats-on/between-worlds

www.barbican.org.uk